It is known that, at the rear of a turbofan turbine engine, the cold flow and the hot flow travel in the same direction toward the downstream of said turbine engine and come into contact with one another. Since the speeds of said flows are different from each other, the result of this is fluid shear of penetration between said flows, said fluid shear generating noise, called “jet noise” in aviation technology.
To attenuate such a jet noise, thought has already been given to generating turbulence at the boundary between said hot flow and said cold flow. It has therefore already been proposed to make recesses in the outlet edge of the hot flow, said recesses being distributed on the periphery of said outlet edge and each of them generally having at least the approximate shape of a triangle, whose base is indistinguishable from said outlet edge and whose apex is in front of this outlet edge. These recesses are usually called “chevrons” in aviation technology.
These known chevrons are effective in attenuating the jet noise; however, they have the disadvantage of generating considerable drag.
In addition, it must be noted that the reduction of the jet noise is truly useful only when the aircraft fitted with said turbine engine is close to the ground with a high speed of said turbine engine, in order not to annoy the people who are in an airport or who reside in the vicinity of the latter. On the other hand, in the cruising phase at high altitude, the attenuation of the jet noise is of only little importance.
Therefore, at cruising speed, the performance of the aircraft is unnecessarily penalized by said chevrons creating increased drag.